In working with enzymes and other biological samples, it is necessary to remove these enzymes or other material from a freezer (-20.degree. C. or below) and then blend them with the biological specimens in the course of experimental procedures. In use, it is a common practice to remove a number of such filled enzyme containing tubes from the freezer and place then in a holding rack where they must remain cold. In order to keep the contents of the microtubes cold, the rack holding them is often placed in an ice bath, but this arrangement may not be satisfactory for several reasons. First of all, the use of an ice bath is untidy, leaving the tubes wet and requiring additional handling. Second, the presence of the water on the tubes may cause contamination and, furthermore, an ice bath often does not keep the contents of the tubes as cold as needed for the operations to which they are subjected. This invention provides means to obviate the above problems.